The invention concerns a piston-pin for liquid cooled pistons having at least one longitudinal bore sealed at its ends by cup shaped sealing elements consisting of a base and a rim, and which are impressed or shrunk into position.
In thermically highly strained internal combustion engines, the pistons are often liquid cooled, specifically with the help of lubricating oils. Such oil flows from a bore in the crankshaft through the connecting rod and passages in the piston-pin to the piston, where it picks up heat in the hollow space of the piston base. From there the oil flows back to the crankcase housing.
Various kinds of piston-pins for liquid cooled pistons are known, among them a piston-pin with a central and several eccentric longitudinal bores, where only the latter are used as access means for the coolant. These eccentric longitudinal bores are sealed at their ends by threaded plugs. Therein two disadvantages cannot be avoided; firstly, the eccentric longitudinal bores weaken the piston pin considerably so that piston-pin failures are not rare, and moreover, the oval deformation of the piston-pin upon ignition while the piston is in the upper position causes the threaded plugs in the longitudinal bores to work free as these massive plugs cannot adjust to the oval deformation of the piston pin containing the longitudinal bore.
A second well known type of construction provides for a relatively thin walled pipe inside a central longitudinal bore of the piston-pin, such pipe having at each end a flange element sealing the longitudinal bore. Such embodiments have the disadvantage not only of being relatively expensive, but also of experiencing frequent transverse breaks of the pipe positioned inside the piston bore as a result of the load variations during operation. Yet further complex is a third known piston-pin (DT-PS 1,301,677) containing a central longitudinal bore which, however, does not serve as a passage for cooling oil; for such latter purposes a longitudinal bore is provided in an eccentric separate threaded pin, which is located within the area of the piston pin, and which extends further into the rod and to two bushings surrounding the piston pin. The longitudinal bore in this threaded pin is sealed at its ends by massive plugs which, as mentioned above, are subject to the danger of working free.
Further, a piston pin containing a sealed central longitudinal bore serving as passage for the cooling oil has become known (GB-PS 1,058,360), in which impressed, slightly warped, flat discs are provided apparently as sealing elements for the piston-pin longitudinal bore. While the thickness of these discs is only approximately 25% of the wall thickness of the piston-pin, it is still, despite its warping, much too stiff in the radial direction to adjust to an adequate degree to the overall deformation of the piston-pin upon ignition while in the upper dead center position. The degree of the radial stiffness must be considered in relation to the high pressure per unit of area between the rim of the discs and the wall of the piston-pin longitudinal bore, such high pressure being inevitable as the results of the disc configuration of such sealing elements. It follows that such sealing elements work free after very brief periods of time, and in fact become ineffective as sealing elements after even shorter periods. This would seem to be the reason why such disc shaped sealing elements have never been used for piston-pins, but only as seals to plug cored holes in crankcase housings of internal combustion engines.
Lastly, a piston-pin for non-liquid cooled pistons is known (DT-PS 689 837) containing a central longitudinal bore the ends of which contain mushroom shaped elements with discs turned toward the outside. These mushroom shaped elements do not, however, seal the piston-pin longitudinal bore as there is an opening in the disc; furthermore, it is not important to secure these mushroom shaped elements within the piston pin, as they must only maintain the piston pin in its proper position within the cylinder, i.e. they act only as spacers, their exteriorly convex shaped discs abutting against the cylinder wall. Since furthermore the wall thickness of the discs of the mushroom formed elements are approximately on the same order as the piston-pin wall thickness, such mushrooms, were one to impress them into a piston pin longitudinal bore for purposes of sealing, would certainly during operation work loose as well.
In experiments with piston-pins of the initially mentioned type, discs of DIN 443 specifications and possessing a uniform wall thickness were first used as sealing elements. These cup shaped sealing elements were secured in the piston-pin longitudinal bore by means of a crease rolled in their rim; in actual operation, however, it turned out that this type of fastening was extremely problematical and that it by no means assured during actual operation that the sealing elements would not work free or form a no longer pressure tight seal in the piston-pin longitudinal bore. Therefore, a metal glue had to be added into the space between the receiving groove and the crease of the sealing element rim in the piston-pin longitudinal bore, and finally the cup shaped sealing elements had to be subjected to extensive heat treatment.